Aqueous ink for mimeograph printing and method for mimeograph printing

ABSTRACT

A water-based ink for stencil printing, which comprises an unsaturated carboxylic acid-based water-soluble polymer and triethylene glycol. The ink preferably further comprises β-thiodiglycol as an optional component.

TECHNICAL FIELD

The present invention relates to a water-based ink for stencil printing,and more particularly to a water-based ink for stencil printing that issuitable for use in a rotary digital stencil printing machine, as wellas a stencil printing method that uses such an ink.

BACKGROUND ART

Compared with other printing methods such as offset printing, gravureprinting, and letterpress printing, stencil printing offers significantadvantages in terms of operability and convenience, including notrequiring complex operations such as post-use cleaning operations, andnot requiring a specialist operator. Since the introduction of thermalstencil making methods that use a thermal head as a perforation device,image processing within stencil printing methods has been able to bedigitalized, enabling high quality printed products to be producedquickly and with comparative ease, and consequently the convenience ofstencil printing continues to gain recognition, even as a method forinformation processing terminals.

Rotary stencil printing machines, in which the making, loading, andremoval operations for the master, as well as the ink supply operationand the printing operation are all controlled automatically, are widelyused in offices and schools under names such as digital stencilduplicators.

Inks for stencil printing have conventionally been water-in-oil (W/O)emulsion inks. W/O emulsion inks have a function that inhibitsvariations in the ink composition or the ink properties when theprinting machine is sitting unused, even if the ink inside the machineis in contact with the atmosphere. In other words, the water, which isthe inner phase component of the emulsion ink, is covered with the outerphase oil component, meaning evaporation of the water is inhibited.

It is thought that the drying of printed material that has been printedusing a W/O emulsion ink proceeds by a mechanism that relies on thepenetration of the ink into the gaps between the fibers of the paperthat functions as the print target (the print medium), and the gradualseparation of the ink into an oil phase and a water phase as a result ofcontact with the paper fibers, thus enabling the water, which representsthe major component of the ink, to contact the atmosphere and evaporate.However, the water within the ink transferred to the print medium isunable to undergo adequate contact with the atmosphere in the shortperiod of time following printing, meaning the drying characteristicsimmediately following printing rely on drying by penetration. However,because the viscosity of a W/O emulsion ink is designed to be relativelyhigh, the rate of penetration is not particularly fast, meaning thedrying characteristics of the ink immediately following printing are notentirely satisfactory.

Improving the drying rate of printed material is an extremely importantproblem for stencil printing. If the printed material is not dry, theoperator is unable to handle the material, and the advantage of stencilprinting of “producing high quality printed material in a short time” ispartially negated.

Accordingly, a variety of improvements have been proposed for enhancingthe drying characteristics of the printed material, and for example,ultraviolet curing inks for stencil printing that undergo fixation anddrying-upon irradiation with ultraviolet light are already known (seeJapanese Laid-Open Publication No. 2002-30238). Furthermore, water-basedinks for stencil printing are also being developed due to their improvedenvironmental friendliness and safety, and a stencil printing method inwhich a base is applied to the printed surface immediately followingprinting, thereby improving the penetration of the water-based ink intothe paper, is already known (see Japanese Laid-Open Publication No.2001-302955).

However, in those cases where a drying method that uses a chemicalreaction is used, an irradiation device for providing the curing energyand an application device for the reaction liquid are required, as isthe energy for those devices, and expensive raw materials must also beincluded within the ink.

On the other hand, with conventional water-based inks for stencilprinting, if the printing machine is left in an unused state, and theink inside the printing machine is left in an open system for anextended period, then the ink loses fluidity. As a result, the printingoperability deteriorates after the printing machine has been leftsitting unused for an extended period, and if the printing machine isnot disassembled and cleaned, either immediately after printing orimmediately prior to recommencing printing, then recommencing printingoperations may become impossible, which significantly impairs theadvantage of stencil printing of providing “favorable operability andworkability”.

Accordingly, an object of the present invention is to provide awater-based ink for stencil printing which exhibits favorableoperability and workability during printing, and exhibits excellentdrying characteristics of the printed material without requiring the useof special devices, apparatus, or energy or the like, such as theprovision of heat, light, or reactive substances, as well as a stencilprinting method that uses such an ink.

DISCLOSURE OF INVENTION

The present invention relates to a water-based ink for stencil printingthat comprises an unsaturated carboxylic acid-based water-solublepolymer and triethylene glycol.

Another aspect of the present invention relates to a stencil printingmethod that uses a water-based ink for stencil printing according to theabove aspect of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A water-based ink for stencil printing (hereafter, the term “water-basedink for stencil printing” is abbreviated as simply “ink”) according tothe present invention comprises water, a water-soluble organic solvent,a colorant, and a thickener, wherein triethylene glycol is added as thewater-soluble organic solvent. From the viewpoint of maintainingfavorable ink fluidity after the printing machine has been left sittingfor an extended period, the quantity of triethylene glycol within theink is preferably at least 12.5% by weight, and is even more preferably15% by weight or higher. Although there are no particular restrictionson the upper limit for the blend quantity of triethylene glycol, inorder to limit image show through, the quantity is preferably no morethan approximately 45% by weight, and even more preferably 35% by weightor less.

In addition to the triethylene glycol, β-thiodiglycol [S(CH₂CH₂OH)₂;2,2′-thiodiethanol] is preferably also incorporated in the ink.Incorporating diethylene glycol is also desirable. In other words,β-thiodiglycol and/or diethylene glycol are preferably used incombination with the triethylene glycol. In such cases, from theviewpoint of maintaining favorable ink fluidity after the printingmachine has been left sitting for an extended period, the combinedquantity of these materials is preferably at least 12.5% by weight, andis even more preferably 15% by weight or higher. Although there are noparticular restrictions on the upper limit for the combined blendquantity of these materials, in order to limit image show through, thecombined quantity is preferably no more than approximately 45% byweight, and even more preferably 35% by weight or less.

In addition, other water-soluble organic solvents may also be used.Examples of these other water-soluble organic solvents include organiccompounds that are liquid at room temperature and soluble in water.Suitable examples include lower alcohols such as methanol, ethanol,1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, and2-methyl-2-propanol; glycols such as ethylene glycol, tetraethyleneglycol, pentaethylene glycol, propylene glycol, dipropylene glycol, andtripropylene glycol; glycerol; acetins (monoacetin, diacetin, andtriacetin); glycol derivatives such as triethylene glycol monomethylether, triethylene glycol monoethyl ether, triethylene glycol monopropylether, triethylene glycol monobutyl ether, tetraethylene glycolmonomethyl ether, tetraethylene glycol monoethyl ether, tetraethyleneglycol dimethyl ether, and tetraethylene glycol diethyl ether; as wellas triethanolamine and sulfolane. Low molecular weight polyalkyleneglycols, including polyethylene glycol with an average molecular weightwithin a range from 190 to 630, such as an average molecular weight of200, 300, 400, or 600, polypropylene glycol diol with an averagemolecular weight within a range from 200 to 600, such as an averagemolecular weight of 400, and polypropylene glycol triol with an averagemolecular weight within a range from 250 to 800, such as an averagemolecular weight of 300 or 700, can also be used. These water-solubleorganic solvents can be used either alone, or in combinations of two ormore different solvents.

Generally it is thought that in an open system, even inside a stencilprinting machine, even a water-soluble organic solvent will graduallyevaporate into the atmosphere, depending on the nature of the solvent,meaning any ink that is left to sit inside a printing machine willeventually solidify. Alternatively, it is thought that a water-solubleorganic solvent will be absorbed into the Japanese paper fibers of anymaster left on the printing machine drum, meaning the ink inside theprinting machine will solidify. In addition, there is the danger thatonce the water has evaporated from the ink, the colorant will aggregate.

In contrast, triethylene glycol does not evaporate into the atmosphere,even if left to sit for extended periods, is resistant to absorptioninto the Japanese paper fibers of any master left on the printingmachine drum, and is able to prevent aggregation of the colorant.Consequently, it is thought that an ink that includes this type ofwater-soluble organic solvent will retain its fluidity and inhibitsolidification, even if left to sit inside the printing machine.

The liquid component of the ink is a mixture of water and thewater-soluble organic solvent. When a water-soluble organic solvent ismixed with water, the viscosity of the mixed liquid is always low,regardless of the size of the viscosity of the water-soluble organicsolvent. In other words, the viscosity of the liquid component of theink is almost unaffected by the viscosity of the water-soluble organicsolvent, and the desired ink viscosity can be obtained whether a lowviscosity water-soluble organic solvent is used or a high viscositywater-soluble organic solvent is used. On the other hand, when the inkis left to sit inside a printing machine and the water evaporates, theviscosity of the liquid component of the ink approaches the viscosity ofthe water-soluble organic solvent. Accordingly, it is thought that byusing triethylene glycol, which represents a water-soluble organicsolvent of low viscosity, any increase in the viscosity of the liquidcomponent of the ink following evaporation of the water can besuppressed, enabling the fluidity of the ink inside the printing machineto be maintained.

From the viewpoint of improving the drying characteristics of theprinted material, water preferably accounts for at least 50% by weight,and even more preferably 65% by weight or more, of the ink. The watercontained within the ink can evaporate into the atmosphere immediatelyfollowing printing. In addition, it is thought that by forcing the inkto penetrate into the gaps between the fibers of the printing paperduring printing, the contact surface area between the ink and the airexpands rapidly within the interior of the printing paper, furtherimproving the evaporation rate of the water, and as a result, increasingthe quantity of water further improves the drying characteristics of theprinted material. Although there are no particular restrictions on theupper limit for the blend quantity of the water, the quantity ispreferably set to ensure a favorable balance with the other componentsof the ink.

The colorant can use either pigments or dyes, or a combination of two ormore such colorants. Suitable pigments include organic pigments such asazo-based pigments, phthalocyanine-based pigments, dye-based pigments,condensed polycyclic pigments, nitro-based pigments, and nitroso-basedpigments (such as brilliant carmine 6B, lake red C, Watchung red, disazoyellow, Hansa yellow, phthalocyanine blue, phthalocyanine green, alkaliblue, and aniline black); inorganic pigments, including metals such ascobalt, iron, chrome, copper, zinc, lead, titanium, vanadium, manganese,and nickel, as well as metal oxides, metal sulfides, yellow ocher,ultramarine, and iron blue pigments; and carbon blacks such as furnacecarbon black, lamp black, acetylene black, and channel black. Suitabledyes include those basic dyes, acid dyes, direct dyes, soluble vat dyes,acid mordant dyes, mordant dyes, reactive dyes, vat dyes, and sulfidedyes that are water soluble, as well as those dyes that have beenconverted to a water-soluble form through reduction or the like. Eitherpigments and/or dyes can be used as the colorant, but the use ofpigments is preferred, as they enable production of an ink that exhibitsminimal bleeding or image show through, and excellent weatherresistance.

The quantity of colorant within the ink is typically within a range from1 to 15% by weight, and preferably from 3 to 12% by weight. In order tomaximize the print density of the printed material, the colorantquantity is preferably at least 5% by weight. Even if the ink contains5% by weight or more of colorant, aggregation of the colorant when theprinting machine is left in an unused state for an extended period canstill be prevented, enabling an improvement in the printing operability.If the quantity of colorant exceeds 15% by weight, then there is adanger that the printing performance may deteriorate after the printingmachine has been left in an unused state.

From the viewpoints of preventing aggregation of the colorant andmaintaining the fluidity of the ink, the quantity of triethylene glycol,or the combined quantity of triethylene glycol, β-thiodiglycol and/ordiethylene glycol is preferably at least twice the weight of thequantity of colorant, and although there are no particular restrictionson the upper limit, the quantity is preferably no more than 20 times,and most preferably from 2.5 to 6.0 times the weight of the colorant.

An unsaturated carboxylic acid-based water-soluble polymer is added as athickener. An unsaturated carboxylic acid-based water-soluble polymerrefers to a water-soluble polymer comprising a repeating unitrepresented by a formula (1) shown below:

(wherein, R¹, R², and R³ each represent, independently, H, CH₃, or(CH₂)_(n)COOH (wherein, n is either 0 or 1)). In those cases where apolymer contains 2 or more carboxyl groups, these carboxyl groups mayalso form an acid anhydride group. In the case of a copolymer, a random,alternate, block, or graft copolymer may be used.

Examples of this unsaturated carboxylic acid-based thickener includewater-soluble polymers comprising, within the principal chain, one ormore unsaturated carboxylic acids selected from the group consisting ofacrylic acid, methacrylic acid, maleic anhydride, maleic acid, fumaricacid, crotonic acid, and itaconic acid, as well as the salts thereof.Specific examples include polyacrylic acid, polymethacrylic acid,polycrotonic acid, polyitaconic acid, polymaleic acid, polyfumaric acid,acrylic acid-methacrylic acid copolymers, acrylic acid-itaconic acidcopolymers, acrylic acid-maleic acid copolymers, acrylic acid-acrylateester copolymers, acrylic acid-methacrylate ester copolymers, andacrylic acid-sulfonic acid-based monomer copolymers. These polymers canbe used either alone, or in combinations of two or more differentpolymers.

Because these unsaturated carboxylic acid-based thickeners areelectrolyte thickeners with a plurality of dissociable groups on sidechains, and are capable of providing the desired thickening effect evenwith small quantities, the blend quantity of the thickener can be keptsmall. Furthermore, even if left to sit inside a printing machine, thethickener does not cause solidification of the ink.

In this description, the unsaturated carboxylic acid-based water-solublepolymer includes not only the unneutralized polymers described above,but also neutral salts of the above polymers. Examples of these neutralsalts include salts of alkali metals such as sodium and potassium,ammonium salts, and salts of alkanolamines such as triethanolamine, andspecific examples of favorable salts include sodium polyacrylate,potassium polyacrylate, ammonium polyacrylate, triethanolaminepolyacrylate, sodium polymethacrylate, ammonium polymethacrylate, sodiumpolyitaconate, sodium polymaleate, the sodium salt of an acrylicacid-methacrylic acid copolymer, and the sodium salt of an acrylicacid-maleic acid copolymer.

The quantity added of the above thickener varies depending on factorssuch as the chemical structure of the thickener and the desired inkviscosity, but in order to achieve stable ink properties, is preferablyat least 0.01% by weight, and in order to ensure a favorable balancewith the other components of the ink and ensure favorable printingoperability following the printing machine being left in an unusedstate, is preferably no more than 5% by weight, and is even morepreferably within a range from 0.05 to 3% by weight, and most preferablyfrom 0.1 to 2% by weight.

The ink may also comprise one or more other water-soluble polymer-basedthickeners or clay mineral-based thickeners, in addition to theaforementioned unsaturated carboxylic acid-based thickener.

Examples of these optional other water-soluble polymer-based thickenersinclude natural polymers, semisynthetic polymers, and syntheticpolymers. Suitable natural polymers include plant-based natural polymerssuch as gum arabic, carageenan, guar gum, locust bean gum, pectin,tragacanth gum, corn starch, konjac mannan, and agar; microbial naturalpolymers such as pullulan, xanthan gum, and dextrin; and animal-basednatural polymers such as gelatin, casein, and animal glue. Suitablesemisynthetic polymers include cellulose-based semisynthetic polymerssuch as ethylcellulose, carboxymethylcellulose, hydroxyethylcellulose,hydroxypropylcellulose, methylcellulose, andhydroxypropylmethylcellulose; starch-based semisynthetic polymers suchas hydroxyethyl starch, sodium carboxymethyl starch, and cyclodextrin;alginate-based semisynthetic polymers such as sodium alginate andpropylene glycol alginate; and sodium hyaluronate. Suitable syntheticpolymers include vinyl-based synthetic polymers such aspolyvinylpyrrolidone, polyvinyl alcohol, polyvinyl methyl ether,poly-N-vinylacetamide, and polyacrylamide; as well as polyethyleneoxide, polyethyleneimine, and polyurethane.

Examples of clay mineral-based thickeners include smectite-based clayminerals such as montmorillonite, hectorite, and saponite.

The blend quantity of these optional thickeners other than theunsaturated carboxylic acid-based thickener is typically no more than10% by weight, and preferably no more than 5% by weight, and mostpreferably 2% by weight or less.

The ink may also include suitable quantities of pigment dispersingagents, fixing agents, antifoaming agents, surface tension reductionagents, pH regulators, antioxidants, and preservatives, in addition tothe components described above.

An alkali-soluble resin may also be added to the ink as a fixing agentfor improving the fixation of the colorant to the print target such asthe printing paper. In those cases where a pigment is used as thecolorant, an alkali-soluble resin can also be used as a pigmentdispersing agent.

Examples of suitable alkali-soluble resins include styrene-acrylic acidcopolymers, styrene-a-methylstyrene-acrylic acid copolymers,styrene-methacrylic acid copolymers, styrene-acrylate ester-acrylic acidcopolymers, styrene-maleic anhydride copolymers,vinylnaphthalene-acrylic acid copolymers, vinylnaphthalene-maleic acidcopolymers, isobutylene-maleic anhydride copolymers, acrylateester-acrylic acid copolymers, methacrylate ester-acrylic acidcopolymers, acrylate ester-methacrylic acid copolymers, methacrylateester-methacrylic acid copolymers, and acrylate ester-methacrylateester-acrylic acid copolymers, and a combination of two or more of theseresins may also be used. These alkali-soluble resins can be neutralizedand converted to a water-soluble form using a suitable alkali, includingan alkali metal hydroxide such as sodium hydroxide or potassiumhydroxide, ammonia water, or an alkanolamine such as triethanolamine.

If a large quantity of alkali-soluble resin is added, then there is adanger of interfering with the printing performance of the printingmachine following a period of non-use, and consequently the quantity ofalkali-soluble resin within the ink, calculated as a solid fractionpercentage, is preferably no more than 5% by weight, and even morepreferably 3% by weight or less.

An oil-in-water (O/W) resin emulsion can also be incorporated within theink, and used as a fixing agent for fixing the colorant to the printingpaper or the like that functions as the print target. In those caseswhere a pigment is used as the colorant, this resin emulsion can also beused as a pigment dispersing agent.

Examples of suitable oil-in-water (O/W) resin emulsions includeemulsions of polyvinyl acetate, ethylene-vinyl acetate copolymers, vinylacetate-acrylate ester copolymers, polyacrylate ester, polymethacrylateester, polystyrene, styrene-acrylate ester copolymers, styrene-butadienecopolymers, vinylidene chloride-acrylate ester copolymers, polyvinylchloride, vinyl chloride-vinyl acetate copolymers, and polyurethane andthe like. Combinations of two or more of these emulsions may also beused.

If a large quantity of resin emulsion is added, then there is a dangerof interfering with the printing performance of the printing machinefollowing a period of non-use, and consequently the quantity of resinemulsion within the ink, calculated as a solid fraction percentage, ispreferably no more than 5% by weight, and even more preferably 2% byweight or less.

The water-soluble polymers listed above as thickeners can also be usedas fixing agents for improving the fixation of the colorant to theprinting paper, depending on the nature and the quantity of the polymer.Furthermore, in those cases where a pigment is used as the colorant, thewater-soluble polymers can also be used as pigment dispersing agents.

Extender pigments may also be added to the ink to improve the imagequality of the printed material.

Examples of suitable extender pigments include white clay, talc, clay,diatomaceous earth, calcium carbonate, barium carbonate, barium sulfate,alumina white, silica, kaolin, mica, and aluminum hydroxide, andcombinations of two or more of these extender pigments may also be used.

If a large quantity of extender pigment is added, then there is a dangerof inhibiting the fixation of the colorant to the print target, andinterfering with the printing performance of the printing machinefollowing a period of non-use, and consequently the quantity of extenderpigment is preferably no more than 5% by weight, and even morepreferably 2% by weight or less.

In addition, anionic surfactants, cationic surfactants, amphotericsurfactants, nonionic surfactants, or polymer-based, silicone-based orfluorine-based surfactants may also be added to the ink as pigmentdispersing agents, antifoaming agents, or surface tension reductionagents or the like.

An electrolyte may also be added to the ink to allow regulation of theink viscosity or pH. Examples of suitable electrolytes include sodiumsulfate, potassium hydrogenphosphate, sodium citrate, potassiumtartrate, and sodium borate, and combinations of two or more of theseelectrolytes may also be used. Other materials such as sulfuric acid,nitric acid, acetic acid, sodium hydroxide, potassium hydroxide,ammonium hydroxide, and triethanolamine and the like may also be used inthe ink as thickening assistants or pH regulators.

By adding an antioxidant, oxidation of the ink components can beprevented, and the storage stability of the ink can be improved.Examples of suitable antioxidants include Lascorbic acid, sodiumL-ascorbate, sodium isoascorbate, potassium sulfite, sodium sulfite,sodium thiosulfate, sodium dithionite, and sodium pyrosulfite.

By adding a preservative, degradation of the ink can be prevented,enabling the storage stability to be improved. Examples of suitablepreservatives include isothiazolone-based preservatives such as5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one,2-n-octyl-4-isothiazolin-3-one, and 1,2-benzoisothiazolin-3-one;triazine-based preservatives such ashexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine; pyridine orquinoline-based preservatives such as sodium 2-pyridinethiol-1-oxide and8-oxyquinoline; dithiocarbamate-based preservatives such as sodiumdimethyldithiocarbamate; organobromine-based preservatives such as2,2-dibromo-3-nitrilopropionamide, 2-bromo-2-nitro-1,3-propanediol,2,2-dibromo-2-nitroethanol, and 1,2-dibromo-2,4-dicyanobutane; as wellas methyl p-hydroxybenzoate, ethyl p-hydroxybenzoate, potassium sorbate,sodium dehydroacetate, and salicylic acid.

An ink comprising the aforementioned components can be produced bymixing the water, the triethylene glycol, the colorant, and theunsaturated carboxylic acid-based water-soluble polymer, together withany of the other optional components described above as desired. Forexample, a portion of the water, the pigment, and the pigment dispersingagent can be mixed together, and a dispersion device such as a ball millor beads mill then used to disperse the pigment, while the remainder ofthe water, the thickener, and the triethylene glycol are also mixedtogether, before the two separate mixtures are then combined and mixed.

The most appropriate range for the ink viscosity varies depending onfactors such as the printing pressure of the printing apparatus, but istypically within a range from approximately 0.5 to approximately 20 Pa·s(the viscosity is measured at 20° C., using a shear rate of 100/s), and(pseudo) plastic flow characteristics are ideal for stencil printing.

An ink of the present invention is able to maintain favorable fluidity,even if the printing machine is left in an unused state for an extendedperiod with the ink exposed in an open system inside the printingmachine, causing the majority of the water within the ink to be lost toevaporation, and consequently, by using this ink, printing can beconducted without the need to disassemble and clean the printing machinebefore or after each printing operation, meaning the printingoperability of the printing machine following a period of non-use can besignificantly improved. In addition, an ink of the present inventionexhibits favorable drying characteristics, and so by using this ink, ahigh quality printed material can be provided that exhibits excellentdrying characteristics and is resistant to smudging even if handledimmediately following printing. The drying principles utilize mainly theproperties of water, and because the drying does not require the use ofspecial devices, apparatus, or energy or the like, such as the provisionof heat, light, or reactive substances, the printing apparatus can bereduced in size, the cost of the ink raw materials can be reduced, andsuperior levels of environmental friendliness and safety can beachieved.

A stencil printing method according to the present invention isconducted using the ink according to the present invention describedabove. Specifically, the method comprises: preparing a stencil master;and pressing the produced stencil master and a print target together,thereby causing the ink of the present invention to pass through theperforated portions of the stencil master and onto the print target.

There are no particular restrictions on the stencil printing machineused, although because of their superior operability, digital stencilprinting machines are preferred.

EXAMPLES

As follows is a more detailed description of the present invention usinga series of examples, although the present invention is in no waylimited by these examples. In the following description, the units “% byweight” are abbreviated simply as “%”.

Example 1

6.0% of carbon black (MCF88, manufactured by Mitsubishi ChemicalCorporation) as a colorant, 1.3% of polyvinylpyrrolidone (K90,manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as a pigmentdispersing agent, and 20.0% of distilled water were mixed together, andwere then dispersed thoroughly using a beads mill, thus yielding apigment dispersion. 0.5% of polyacrylic acid (Junlon PW150, manufacturedby Nihon Junyaku Co., Ltd.) as a thickener was then dissolved in 16.0%of distilled water, and following neutralization of the resultingsolution by addition of 10.0% of a 2% aqueous solution of sodiumhydroxide, the neutralized solution was combined with the previouslyprepared pigment dispersion, 16.0% of triethylene glycol, and theremaining quantity of distilled water (30.2%), and the resultingcombination was then mixed thoroughly, yielding an ink of the example 1.

Examples 2 to 6, Comparative Examples 1 to 4

With the exception of using the compositions shown in Table 1, inks foreach of the examples and comparative examples were prepared in the samemanner as the example 1.

Comparative Example 5

6.0% of carbon black (the same as the example 1) as a colorant, 1.3% ofpolyvinylpyrrolidone (the same as the example 1) as a pigment dispersingagent, and 20.0% of distilled water were mixed together, and were thendispersed thoroughly using a beads mill, and to the resulting dispersionwere added 0.7% of sodium sulfate as an electrolyte, 4.0% of glycerol asa water-soluble organic solvent, and 46.0% of distilled water, thusyielding a water phase. Meanwhile, a combination of 4.0% of Sunsen oil4240 (manufactured by Japan Sun Oil Company Ltd.) and 14.0% of AFsolvent No. 6 (manufactured by Nippon Oil Corporation) as an oilcomponent, and 4.0% of sorbitan sesquioleate as an emulsifying agentwere mixed together, thereby yielding an oil phase. The water phase wasthen added gradually to the oil phase and emulsified, thus yielding aW/O emulsion ink for stencil printing.

Using each of the inks (the water-based inks for stencil printing)prepared in the examples 1 to 6 and the comparative examples 1 to 4, andthe emulsion ink for stencil printing prepared in the comparativeexample 5, printing was conducted onto printing paper (Riso lightweightpaper, manufactured by Riso Kagaku Corporation) using a stencil printingmachine (Risograph RP370, manufactured by Riso Kagaku Corporation), andthe drying characteristics of the obtained printed material wasevaluated. Furthermore, using each of the inks, the printing machine wasleft to stand in an unused state for a certain period of time followingthe completion of printing, and the printing was then recommenced, andthe printing characteristics on printing recommencement were evaluated.The results of the evaluations for each ink are shown in Table 1.

The drying characteristics were evaluated by touch, and an evaluation ofA was recorded if the finger was not soiled even when the printedmaterial was touched 10 seconds following completion of printing, anevaluation of B was recorded if the finger was not soiled after 30seconds, and an evaluation of C was recorded if the finger was soiledeven 30 seconds after the completion of printing.

The operability of the printing machine following a period of non-usewas evaluated as A if printing could be recommenced withoutdisassembling and cleaning the printing machine, and evaluated as C iscleaning was required. TABLE 1 Example Comparative Example Blendquantity/% by weight 1 2 3 4 5 6 1 2 3 4 5 Colorant Carbon black 6.0 5.08.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 Pigment Polyvinylpyrrolidone 1.3 1.3 1.31.3 1.3 1.3 1.3 1.3 1.3 1.3 dispersing agent Water Distilled water 76.066.0 63.0 58.0 70.0 70.0 76.0 48.0 76.0 74.0 Water-soluble Triethyleneglycol 16.0 27.0 27.0 34.0 12.0 12.0 — — — 16.0 organic solventβ-thiodiglycol — — — — 10.0 — — — — — Diethylene glycol — — — — — 10.0 —— — — Ethylene glycol — — — — — — 16.0 44.0 — — Glycerol — — — — — — — —16.0 — Thickener Polyacrylic acid 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 —Sodium alginate — — — — — — — — — 2.7 pH regulator Sodium hydroxide 0.20.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 — Evaluation of Drying characteristics AA B B A A A C A A C printability Operability after 3 days unused A A A AA A C A C C A Operability after 10 days unused A A A A A A — C — — AOperability after 1 month unused A A A A A A — — — — A

The inks of the examples all exhibited excellent drying characteristicsof the printed material, and the printing machine was able to beoperated even after sitting unused for 1 month.

In contrast, with the inks from the comparative examples 1 to 4, if theprinting machine was left in an unused state, then it became inoperablewithin a short period of time. In the comparative example 2, a largequantity of water-soluble organic solvent was included in the ink, butthe printability did not improve. Furthermore, despite containing alarge quantity of water (66.0%), the emulsion ink of the comparativeexample 5 produced printed material for which the drying characteristicswere slow.

1. A water-based ink for stencil printing, comprising an unsaturatedcarboxylic acid-based water-soluble polymer and triethylene glycol. 2.The water-based ink for stencil printing according to claim 1, furthercomprising β-thiodiglycol.
 3. The water-based ink for stencil printingaccording to claim 1, further comprising diethylene glycol.
 4. A stencilprinting method that uses the water-based ink for stencil printingaccording to claim
 1. 5. The water-based ink for stencil printingaccording to claim 2, further comprising diethylene glycol.
 6. A stencilprinting method that uses the water-based ink for stencil printingaccording to claim
 2. 7. A stencil printing method that uses thewater-based ink for stencil printing according to claim 3.